The first aim of the project is to test the physiological implications of our earlier finding that in vitro development of erythroblasts is stimulated by N-tetracosanoyl sphingosine and N-15-tetracosenoyl sphingosine. A hypothesis is put forward on the basis of these findings and other available data, that red cell maturation in vivo depends upon the presence in the plasma of ceramides and/or sphingomyelins containing C24-carboxylic acid residues. This hypothesis will be tested directly by comparing the metabolism of labeled C24 and shorter chain acids, with that of the corresponding ceramides in marrow cell incubations and in normoblasts isolated from the marrow by density centrifugation techniques. Another approach to the problem will involve the study of congenital anemias in man and in mice in which the salient feature is a hypoplasia which could result from either a lack of the essential plasma sphingolipid or a deficit in their utilization by the erythroid precursors. The project will utilize conventional radio-labeling methods, gas liquid chromatographic separations, GCMS analysis and other analytical techniques available from the literature or already established in our laboratory. The project will use extensive consultation and collaborative arrangements with leading hematologists and a leading expert in mass spectrometry.